Image flipping in NSCell and subclasses

[Fred Kiefer]

Hi Alexander,

since your change to the image drawing code the arrow in a NSBrowserCell 
is drawn wrong for the xgps backend (I don't know about the other 
backends, but for win32 all the imaes should be wrong now). While 
looking at this I had the impression that all the flip corrections for 
image drawing in NSCell and it subclasses should be removed. As I don't 
want to investigate this issue into too much detail I would be glad, if 
you could shed some light on this and make clear which of this is still 
needed and why.

Cheers
Fred